U.S. patent application number 10/175205 was filed with the patent office on 2003-01-02 for ink jet recording apparatus.
This patent application is currently assigned to Toshiba Tec Kabushiki Kaisha. Invention is credited to Kusunoki, Ryutaro.
Application Number | 20030001912 10/175205 |
Document ID | / |
Family ID | 19030359 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030001912 |
Kind Code |
A1 |
Kusunoki, Ryutaro |
January 2, 2003 |
Ink jet recording apparatus
Abstract
An ink jet recording apparatus according to the present
invention includes a pressure chamber stored with ink, a nozzle
communicating with the pressure chamber and capable of discharging
the ink from the pressure chamber, and an actuator for increasing
and reducing the capacity of the pressure chamber in response to
driving signals from a driving signal generator. The driving signal
generator successively generate, an expansion pulse for increasing
the capacity of the pressure chamber and a contraction pulse for
reducing the capacity of the pressure chamber with a timing such
that a time lag between the respective centers of the expansion
pulse and the contraction pulse matches the resonance period of a
meniscus generated in the nozzle by the ink in the pressure
chamber. Thus, the ink jet recording apparatus continuously
discharges a plurality of ink drops through the nozzle to form a
pixel.
Inventors: |
Kusunoki, Ryutaro;
(Mishima-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
Toshiba Tec Kabushiki
Kaisha
Tokyo
JP
|
Family ID: |
19030359 |
Appl. No.: |
10/175205 |
Filed: |
June 19, 2002 |
Current U.S.
Class: |
347/11 |
Current CPC
Class: |
B41J 2/04588 20130101;
B41J 2/04595 20130101; B41J 2/04581 20130101 |
Class at
Publication: |
347/11 |
International
Class: |
B41J 029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2001 |
JP |
2001-191800 |
Claims
What is claimed is:
1. An ink jet recording apparatus comprising: a pressure chamber
stored with ink; a nozzle communicating with the pressure chamber
and capable of discharging the ink from the pressure chamber; an
actuator for increasing and reducing the capacity of the pressure
chamber in response to driving signals and continuously discharging
a plurality of ink drops through the nozzle to form a pixel; and a
driving signal generator for successively generating, an expansion
pulse for increasing the capacity of the pressure chamber and a
contraction pulse for reducing the capacity of the pressure chamber
with a timing such that a time lag between the respective centers
of the expansion pulse and the contraction pulse substantially
corresponds to the resonance period of a meniscus generated in the
nozzle by the ink in the pressure chamber.
2. An ink jet recording apparatus according to claim 1, further
comprising a temperature detector for detecting the temperature of
the ink in the pressure chamber, and wherein the driving signal
generator compensates the time lag between the respective centers
of the expansion pulse and the contraction pulse as the resonance
period changes according to the temperature detected by the
temperature detector.
3. An ink jet recording apparatus according to claim 1, wherein the
width of the expansion pulse is adjusted to half of the resonance
period of the meniscus generated in the nozzle.
4. An ink jet recording apparatus according to claim 2, wherein the
width of the expansion pulse is adjusted to half of the resonance
period of the meniscus generated in the nozzle.
5. An ink jet recording apparatus according to claim 1, wherein the
width of the contraction pulse is shorter than the width of the
expansion pulse.
6. An ink jet recording apparatus according to claim 1, wherein the
voltage of the contraction pulse is lower than the voltage of the
expansion pulse.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2001-191800, filed Jun. 25, 2001, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an ink jet recording
apparatus for gradational printing such that a plurality of ink
drops are continuously discharged through nozzles.
[0004] 2. Description of the Related Art
[0005] Conventionally known is an ink jet recording apparatus in
which an actuator composed of an electromechanical transducer such
as an piezoelectric element is operated by means of driving signals
to increase or reduce the capacity of a pressure chamber that is
stored with ink, whereby the ink is discharged through nozzles to
print a pixel by gradation. Ink jet recording apparatuses of this
type are described in Jpn. Pat. Appln. KOKAI Publication No.
4-250045 and U.S. Pat. No. 5,461,493, for example.
[0006] In the ink jet recording apparatus described in Jpn. Pat.
Appln. KOKAI Publication No. 4-250045, the voltage or pulse width
of driving signals is changed to vary the volume of each ink drop
that is discharged through a nozzle, whereby the dot size of each
ink drop that is dashed against a recording medium can be changed
for gradational printing.
[0007] In the ink jet recording apparatus described in U.S. Pat.
No. 5,461,493, the number of driving pulses is controlled to
discharge a plurality of ink droplets through nozzles and change
the number of droplets to be discharged, whereby the dot size of
each ink drop that is dashed against a recording medium can be
changed for gradational printing.
[0008] In the case of the former gradational printing, it is hard
considerably to change the volume of each discharged ink drop.
Therefore, the latter gradational printing is superior to the
former one in changing the dot size at a high rate.
[0009] In the latter gradational printing, compared with the former
one in which the volume of one discharged ink drop is controlled to
form one pixel, however, a plurality of ink droplets must be
discharged at a higher driving frequency. In order to prevent
lowering of the speed of the latter gradational printing,
therefore, the droplets must be discharged by means of driving
pulses with a considerably high frequency.
[0010] If these driving pulses are continuously applied to the
actuator, vibration of meniscuses in the nozzles that are generated
by means of driving pulses for discharging directly preceding ink
droplets is followed by vibration of meniscuses that are generated
by means of driving pulses for discharging subsequent droplets.
Accordingly, the vibration of the meniscuses becomes so intensive
and disturbing that ink in the nozzles involves air bubbles. If the
ink in the nozzles thus involves air bubbles, the speed of
discharge of ink drops lowers, and in some cases, no ink drops can
be discharged.
BRIEF SUMMARY OF THE INVENTION
[0011] The object of the present invention is to provide an ink jet
recording apparatus capable of minimizing the possibility of ink in
nozzles involving air bubbles even when gradational printing is
carried out in a manner such that a plurality of ink droplets are
continuously discharged to change the dot size.
[0012] An ink jet recording apparatus according to an aspect of the
invention comprises a pressure chamber stored with ink, a nozzle
communicating with the pressure chamber and capable of discharging
the ink from the pressure chamber, an actuator for increasing and
reducing the capacity of the pressure chamber in response to
driving signals and continuously discharging a plurality of ink
drops through the nozzle to form a pixel, and a driving signal
generator for successively generating, an expansion pulse for
increasing the capacity of the pressure chamber and a contraction
pulse for reducing the capacity of the pressure chamber with a
timing such that a time lag between the respective centers of the
expansion pulse and the contraction pulse matches the resonance
period of a meniscus generated in the nozzle by the ink in the
pressure chamber.
[0013] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0015] FIG. 1 is a view showing the configuration of the principal
mechanism of an ink jet recording apparatus according to an
embodiment of the invention;
[0016] FIG. 2 is a sectional view of an ink jet head taken along
line II-II of FIG. 1;
[0017] FIG. 3 is a diagram showing the configuration of a driving
signal generator of the ink jet head;
[0018] FIG. 4 is a waveform showing an example of a driving signal
generated from the driving signal generator;
[0019] FIG. 5A is a diagram showing a meniscus in an initial
state;
[0020] FIG. 5B is a diagram showing a meniscus in a state of 0.5 Tc
after start of operation;
[0021] FIG. 5C is a diagram showing a meniscus in a state of Tc
after start of operation;
[0022] FIG. 5D is a diagram showing a meniscus in a state of 1.5 Tc
after start of operation;
[0023] FIG. 6 is a graph showing change of ink pressure in a
pressure chamber;
[0024] FIG. 7 is a graph showing the relation between driving
voltage and a time lag between the respective centers of expansion
and contraction pulses obtained when seven ink drops are
continuously discharged;
[0025] FIG. 8 is a waveform showing another example of the driving
signal generated from the driving signal generator;
[0026] FIG. 9 is a graph showing the relation between the
respective speeds of discharge of ink drops at which ink is
continuously discharged a plurality of times to form one pixel;
[0027] FIG. 10 is a waveform showing still another example of the
driving signal generated from the driving signal generator; and
[0028] FIG. 11 is a waveform showing a further example of the
driving signal generated from the driving signal generator.
DETAILED DESCRIPTION OF THE INVENTION
[0029] An embodiment of the present invention will now be described
with reference to the accompanying drawings.
[0030] FIGS. 1 and 2 are views showing the configuration of the
principal mechanism of an ink jet recording apparatus. In these
drawings, numeral 1 denotes an ink jet head 1. FIG. 2 is a
sectional view taken along line II-II of FIG. 1.
[0031] The ink jet head 1 is formed by dividing a plurality of
pressure chambers 11 for ink storage by means of partition walls
12. Each pressure chamber 11 is provided with a nozzle 13 for
discharging ink drops. The base of each pressure chamber 11 is
formed of a vibration plate 14. A piezoelectric member 15 is fixed
on the base side of the vibration plate 14 corresponding to each
pressure chamber 11. The vibration plate 14 and the piezoelectric
member 15 constitute an actuator.
[0032] The ink jet head 1 is formed having a common pressure
chamber 16 that communicates with each pressure chamber 11. Ink is
injected from an ink supply unit (not shown) into the chamber 16
through an ink supply port 17, whereby the common pressure chamber
16, pressure chambers 11, and nozzles 13 are filled with ink. As
the pressure chambers 11 and the nozzles 13 are filled with ink, a
meniscus of ink is formed in each nozzle 13. Further, a temperature
sensor 18 as a temperature detector is attached to the back of the
common pressure chamber 16.
[0033] FIG. 3 is a block diagram showing the configuration of the
principal mechanism of a driving signal generator 2 for driving the
ink jet head 1. The principal mechanism of the generator 2 is
composed of a printer controller 21, image memory 22, print data
transfer block 23, and head driver 24.
[0034] The printer controller 21 loads the image memory 22 with
print data and controls the print data transfer block 23 to
transfer image data stored in the memory 22 to the head driver 24.
The head driver 24 is controlled by the printer controller 21 to
drive the ink jet head 1. Temperature information detected by the
temperature sensor 18 is supplied to the printer controller 21.
[0035] If a driving signal is generated from the head driver 24 and
applied to the piezoelectric member 15, according to this
configuration, the piezoelectric member 15 displaces the vibration
plate 14 to change the capacity of the pressure chamber 11.
Thereupon, pressure waves are generated in the pressure chamber 11
to discharge ink drops through the nozzles 13. The resonance period
of the ink meniscus in each nozzle 13 is equal to the Helmholtz
resonance period of ink.
[0036] In the case where gradational printing is carried out
according to the discharge frequency of ink droplets, the volume of
ink droplets discharged in each cycle of operation should
preferably be reduced to obtain high print quality. The shorter the
Helmholtz resonance period of ink in the pressure chamber 11,
moreover, the more quickly the ink drops can be discharged.
[0037] Since the Helmholtz resonance period of ink in the pressure
chamber 11 can be increased by reducing the capacity of the chamber
11, it is to be desired that the capacity of the chamber 11 should
be small enough.
[0038] FIG. 4 is a waveform showing an example of a driving signal
that is generated from the driving signal generator 2. This driving
signal is formed of driving pulses each including an expansion
pulse P1 for increasing the capacity of the pressure chamber 11, a
latency t, and a contraction pulse P2 for reducing the capacity of
the pressure chamber 11. The gradational printing is carried out
with the number of ink drops to be discharged through the nozzles
13 controlled according to the number of the driving pulses. A
fixed delay time is set between the driving pulses.
[0039] If the Helmholtz resonance period of ink or the resonance
period of the ink meniscus is defined as Tc, a time lag between the
respective centers of the expansion pulse P1 and the contraction
pulse P2 is adjusted to Tc. Further, the pulse width of the
expansion pulse P1 and the contraction pulse P2 is adjusted to
Tc/2. Therefore, t is also adjusted to Tc/2.
[0040] Since the resonance period Tc of the ink meniscus changes
depending on temperature, the time lag between the expansion pulse
P1 and the contraction pulse P2 can be compensated according to the
temperature detected by the temperature sensor 18. The printer
controller 21 is provided with TABLE 1, for example, and serves to
correct the time lag between the expansion pulse P1 and the
contraction pulse P2 according to the resonance period Tc that
corresponds to the temperature detected by the temperature sensor
18.
1 TABLE 1 Temperature Tc 10.degree. C. 4.4 .mu.s 20.degree. C. 4.5
.mu.s 30.degree. C. 4.6 .mu.s 40.degree. C. 4.7 .mu.s
[0041] If the resonance period Tc of the ink meniscus changes
depending on the ink temperature, therefore, the time lag between
the respective centers of the expansion pulse P1 and the
contraction pulse P2 can be compensated correspondingly.
Accordingly, the time lag between the respective centers of the
expansion pulse P1 and the contraction pulse P2 can always be
adjusted to the resonance period Tc of the ink meniscus.
[0042] The operation will now be described with reference to FIGS.
5A, 5B, 5C, 5D and 6.
[0043] If the expansion pulse P1 is applied to the piezoelectric
member 15 in an initial state such that an ink meniscus m in each
nozzle 13 is in the state shown in FIG. 5A, the pressure chamber 11
expand so that the ink pressure in the pressure chamber lowers in
the manner shown in FIG. 6. Thereupon, the ink meniscus m receives
a negative pressure from the pressure chamber 11 and starts to
recede, as shown in FIG. 5B.
[0044] Thereafter, the ink pressure in the pressure chamber 11 is
increased to become a positive pressure by pressure vibration in
the manner shown in FIG. 6. In a time equal to 0.5 Tc after the
start of operation, the ink meniscus m receives the positive
pressure from the pressure chamber and ceases to recede, thereby
coming to a standstill. Since the extension pulse P1 then also
terminates, the pressure chamber 11 contracts. When the pressure
chamber 11 starts to contract, the ink pressure further increases
to the highest level, whereupon the meniscus m receives the high
pressure and is discharged through the nozzle 13.
[0045] Thereafter, the ink pressure in the pressure chamber 11 is
lowered by pressure vibration. In a time equal to Tc after the
start of operation, the discharge of the meniscus m terminates
under the negative pressure from the pressure chamber 11. At this
point of time, the meniscus m is in the state shown in FIG. 5C. The
ink discharge through the nozzle 13 is continued by inertia.
[0046] When the time Tc elapses after the start of operation,
application of the contraction pulse P2 is started. Thereupon, the
capacity of the pressure chamber 11 is reduced so that the ink
pressure increases, and the negative pressure lowers. Thereafter,
the meniscus m receives the negative pressure from the pressure
chamber 11 and recedes, whereupon the ink pressure is increased by
pressure vibration.
[0047] In a time equal to 1.5 Tc after the start of operation, the
meniscus m receives the positive pressure from the pressure chamber
11, recedes, and then comes to a standstill. At this point of time,
the meniscus m is in the state shown in FIG. 5D. The ink discharge
through the nozzle 13 is further continued by inertia, and a first
ink drop is discharged. Since the contraction pulse P2 then also
terminates, the pressure chamber 11 expands. When the pressure
chamber 11 starts to expand, the ink pressure lowers, whereupon
most of the pressure generated for the ink discharge is canceled.
Thus, sudden advance of the meniscus m is restrained, so that
Involution of air bubbles can be prevented.
[0048] If the next driving pulses are continuously applied,
thereafter, the process of operation in the initial state and the
subsequent processes are repeated. In the operation for discharging
the second ink drop and the subsequent ink drops, the meniscus
temporarily recedes much deeper than in the case of the discharge
of the first ink drop. Since the ink is supplied from the common
pressure chamber 16 to the pressure chamber 11 owing to the surface
tension of the meniscus, however, the meniscus never continues to
recede if the ink drop discharged in the first cycle of operation
is small.
[0049] FIG. 7 is a graph showing the relation between a driving
voltage V and a time lag between the respective centers of the
expansion and contraction pulses P1 and P2 obtained when seven ink
drops are continuously discharged. Curves g1 and g2 represent the
upper and lower limits, respectively of the operating voltage.
[0050] The lower limit of the operating voltage is the lower limit
of the driving voltage at which normal printing can be carried out.
If the driving voltage is lower than this lower limit, the speed of
discharge of ink drops is so low that the positions of impact of
the ink drops vary substantially, and the printing density is too
low to maintain satisfactory print quality. On the other hand, the
upper limit of the operating voltage is the upper limit of the
driving voltage at which the operation can be performed with
stability. If the driving voltage exceeds this upper limit, the ink
in the pressure chamber 11 involves air bubbles, so that ink drops
cease to be discharged.
[0051] Further, the graph of FIG. 7 indicates that the highest
driving voltage can be used for the drive when the time lag between
the respective centers of the expansion and contraction pulses P1
and P2 is equal to Tc or the resonance period of a meniscus that is
generated in each nozzle. This implies that the ink drops can be
discharged at high speed with the least air bubbles involved when
the time lag between the respective centers of the expansion and
contraction pulses P1 and P2 is equal or approximate to Tc. Even if
the time lag between the respective centers of the expansion and
contraction pulses P1 and P2 is somewhat deviated from Tc,
according to this graph, moreover, a relatively high driving
voltage can be used for the drive in a relatively wide range,
especially in the region higher than Tc, so that the same function
and effect can be obtained.
[0052] It is to be desired, therefore, that the expansion and
contraction pulses P1 and P2 should be generated so that the time
lag between their respective centers is equal to Tc. However, the
time lag need not always be equal to Tc, and may be somewhat
deviated from Tc. In short, it is necessary only that the expansion
and contraction pulses P1 and P2 be generated so that the time lag
between their respective centers substantially corresponds to the
resonance period of the meniscus in each nozzle.
[0053] According to this embodiment, the ink jet recording
apparatus can minimize the possibility of the ink in the nozzles 13
involving air bubbles when one pixel is subjected to gradational
printing by continuously supplying the actuator with a plurality of
driving signals such that the time lag between the respective
centers of the expansion and contraction pulses PI and P2 is made
substantially equal to the resonance period Tc of the meniscus.
[0054] Further, the ink jet recording apparatus can correct the
time lag Tc between the respective centers of the expansion and
contraction pulses PI and P2 in accordance with temperature
information that is detected by the temperature sensor 18.
[0055] Although the driving pulses each of which is composed of the
extension pulse P1 with the pulse width equal to Tc/2, the latency
Tc/2, and the contraction pulse P2 with the pulse width equal to
Tc/2 and which are repeatedly generated with the fixed delay time
have been described as an example of the driving signal that the
driving signal generator 2 generates, the present invention is not
limited to these signals.
[0056] As shown in FIG. 8, for example, the driving signal
generated from the driving signal generator 2 may be formed of
driving pulses that are repeatedly generated without any delay time
between them. In this case, generation of the contraction pulse P2
of one driving pulse is immediately followed by generation of the
extension pulse P1 of another driving pulse.
[0057] If the delay time between the driving pulses is 0, as shown
in FIG. 8, moreover, the speed of discharge of ink drops tends to
increase according to number of ink drop, as indicated by curve g3
of FIG. 9.
[0058] To cope with this, a contraction pulse P2' with a pulse
width shorter than Tc/2 may be used as the contraction pulse
without changing the position of its center, as shown in FIG. 10.
Alternatively, a contraction pulse P2" with a voltage V2 that is
lower than the voltage V1 of the extension pulse P1 may be used as
the contraction pulse, as shown in FIG. 11.
[0059] A moderate increase of the discharge speed allows an ink
drop discharged at a time to unite with its preceding ink drop in
the air, thereby improving the circularness of dots dashed against
a printing medium. If the discharge speed is increased too much,
however, the discharge sometimes may be unstable. In this case, it
is necessary only that the pulse width or voltage of the
contraction pulse be narrowed or lowered to restrain the increase
of the discharge speed. By doing this, the increase of the speed of
discharge of subsequent ink drops can be restrained to maintain the
stability of the ink drop discharge, as indicated by curve g4 of
FIG. 9.
[0060] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *